1. Field of the Invention
The invention relates to a system and a method for receiving and discriminating unique codes from multiple transmitters. More particularly, the invention relates to an event-based system and method for receiving unique codes from multiple transmitters, such as tire pressure sensors, and building a table of those unique codes so that data received from the remote sources can be identified and validated.
2. Related Art
With the development of systems monitoring equipment for vehicles, it is known to monitor the pressure in a vehicle's tires by installing a transducer within each vehicle tire which can provide a perceptible indication of the pressure to the vehicle operator. These indications have included: a visible signal provided on the tire whereby the tire must be visually inspected by the operator, a magnetic field generated by the transducer which generates a warning on the instrument panel for the operator via a detector hard wired near the tire, and a radio transmitter interconnected to the transducer within each tire which provides a wireless signal to a receiver on the vehicle for providing a warning to the operator.
In the wireless tire pressure sensing and indication system mentioned above, transmitters are mounted within each tire which communicate with a receiver. The receiver is interconnected with a display device which can display whether any of the four tires has a low pressure condition. In order to distinguish between each of the tire-mounted transmitters, each of the transmitters is coded with a unique identification number (ID) indicating a particular tire position. Each of the transmitters thereby transmits a data frame containing both the ID and a signal corresponding to the pressure in the particular tire.
Because vehicles are often located nearby one another during operation, it is conceivable that the receiver could detect a signal from a neighboring vehicle and erroneously record the pressure signal as relating to the vehicle in which the receiver is mounted. Further, erroneous signals could also be recorded when the tires are rotated. Yet, further erroneous signals may result if the ID data is corrupted in a volatile memory location. It has been found to be important that a wireless tire pressure monitoring system be able to "learn" the IDs of the tire pressure transmitters associated with the vehicle.
Various solutions have been proposed to the problem of enabling the receiver to learn the IDs. One solution requires the operator of the vehicle to hold a magnet adjacent to each tire which causes the transmitter associated therewith to "wake up" and send a transmission containing the ID to the receiver. Another solution is proposed in U.S. Pat. No. 5,612,671, issued Mar. 18, 1997, titled "Method of Learning Tire Pressure Transmitter ID" ("the '671 patent"), wherein the receiver includes a microprocessor controller programmed to learn the IDs of the tire senders by recording the IDs in the controller memory as "main" senders presumed to be those on the vehicle wheels wherein subsequent new IDs are accepted as "reserve" senders. The '671 patent, however, detects faulty transmitters by measuring the number of transmission failures over a predetermined time period; transmission failures for every ID during the time period are stored as flags, and detection of faulty transmitters is conducted only after the time period expires for a given cycle. Because different transmitters often send signals at different rates, the predetermined time period selected in the '671 system may not be compatible with a particular set of transmitters, making the system less reliable. Thus, the effectiveness of the '671 system depends on the compatibility between the transmission rate of the transmitters and the predetermined time period in the system. If the predetermined time period is not adjustable by the user, this restriction unduly limits the user's selection of transmitters because the selected transmitter's transmission rate must be compatible with that time period.
There is a need for a time-independent, event-based system that operates independently of the transmission rate of the transmitters being sensed.